I’ve raised this before, but that was in the Kodi v19 testing thread, which has now been locked. I think this deserves to be in a still-open, bumpable thread…
First, a link to some of my test clips: Dropbox - Deinterlacing test patterns - Simplify your life
Here’s an approximate copy of what I said in the other thread, edited for clarity:
Star by turning off hardware decoding, then play the 1080i60 wedge pattern clip. Decoded in software, it plays perfectly - that gives you a reference. Now try playing it with hardware decoding, and with deinterlacing set to Auto-Select. If you look carefully, you can see two different sets of artefacts: at the left edge of the horizontal wedge, centred on the 540 mark, there’s some very obvious moiré (this is the result of a deinterlacing error -not what’s interesting here); further to the right within that wedge, you should see also a couple of diagonal bars which sweep left to right, turn till they’re vertical, keep turning till they’re diagonal again, sweep right to left, disappear, and then repeat the cycle - that’s what we’re interested in.
If you now switch deinterlacing to Off, it fixes the deinterlacing, and the main moiré at the 540 mark vanishes; but the sweeping diagonal bars are still there (but fainter). This (I’m fairly sure) is the result of a decoding error.
My “Little Dorrit” clip also shows what look like decoding errors, although they’re more subtle here. To play it as well as possible you’ll need to whitelist 1080p/25, start playing the clip, set deinterlacing to Off, stop, then play it again. This gives correct deinterlacing, but there’s still some definite loss of detail - you notice it in the fine texture of the men’s faces. (For comparison, try playing it on a Pi 2 or 3, running Kodi v18, using MMAL, with VC-1 acceleration enabled, and with deinterlacing set to Off. Much more skin detail is visible.)